This invention relates generally to circuit breakers having a thermally operated snap acting bimetallic actuator and more particularly to a low cost miniature circuit breaker having, a thermally operated snap acting bimetallic actuator of the cycling or non-cycling type, for limiting the electrical overload in a given current carrying circuit and adapted for easy replacement or for retrofitting in place of the conventional blade or clip type fuses, in any given current carrying circuit.
The use in electrical circuits of a thermally operated snap acting bimetallic actuator having, a first member with a contact movable from, a normally closed contacting position with another generally stationary contact on a second member, to an open position with respect to said stationary contact for limiting the flow of current in the electrical circuit, is a known expedient in the prior art.
Such devices are shown in U.S. Pat. Nos. 2,503,008; 3,422,384; 4,068,203 and 4,379,278.
Few of these prior art devices employ the so called "Taylor Blade" bimetallic actuator as shown in U.S. Pat. No. 2,503,008 which produces its snapping action due to increasing contact pressure under changing conditions of current overload in the associated electrical system and has appreciable amplitude of movement from the closed to open position and vice versa.
The use in prior art circuit breakers of these thermally operated snap acting bimetallic actuators requires either relatively large housings which limit their application, or alternatively if smaller housings are used the reduced limited or variations in the travel of the bimetallic actuator results in reduced sensitivity and intolerance to current overload in the associated current carrying circuit and/or arcing of coacting contacts which leads to destruction and failure of the circuit breaker as a protection for the associated current carrying circuit.
The use of circuit breakers with a thermally operated snap acting bimetallic actuator for current limiting in automobiles, trucks, marine engines and related vehicular fields have been minimal due largely to the small size and terminal configuration required to use or retrofit such circuit breakers as a low cost replacement for the relatively new blade or clip type conventional fuses now used.
Some prior art devices to meet this problem provide circuit breakers having a cantilevered thermally operated bimetallic actuator. However, such cantilevered bimetallic actuators were found to be inherently unstable and erratic due to slow opening and minimal amplitude of movement of the coacting contacts which limitations on overload tend to create arcing and sticking of the coacting contacts. Further, in order to convert circuit breakers with such cantilevered type bimetallic actuators from cycling type operation to the non-cycling type operation, a heater wire is added or incorporated to provide an auxiliary source of heat to prevent the bimetallic element of the bimetallic actuator from cooling too rapidly, thus permitting the coacting contacts of the bimetallic actuator to remain open for a longer period of time to in turn prevent the circuit breaker from moving to the normally closed position.
Additionally, circuit breakers having cantilevered type bimetallic actuators which are of the cycling type have bimetallic sensing elements which by necessity, due to the purpose and function of the circuit breaker, are relatively heavy and thick. Such sensing elements during a malfunction such as a short circuit, do not provide the fail safe condition which is desirable when an electrical overload occurs in the circuit. An obviously dangerous condition. In those circuit breakers with a cantilevered type bimetallic actuator which have an auxiliary heating wire to provide a non-cycling type of operation, should the heating wire fail due to a poor weld or other conditions, the circuit breaker will revert to a cycling type of operation and the same dangerous condition on direct short circuit or high overload conditions is then created once again.
Most of these prior art circuit breakers, such as the circuit breakers with cantilevered type bimetallic actuators, have no visual indication of an overload condition nor coacting manual means for resetting the circuit breaker when the overload condition has occurred.
In U.S. Pat. No. 4,379,278, a circuit breaker is shown having a "Taylor Type" thermally operated snap acting bimetallic actuator. In operation, the bimetallic element on the "Taylor Type" bimetallic actuator due to increasing contact pressure during an increase in current will under adverse conditions in the current carrying circuit, at the calibrated trip or snap to open point, move the coacting contacts from the normally closed position to an open position with the appreciable amplitude characteristic of the "Taylor Type" bimetallic actuators.
If the device as shown in U.S. Pat. No. 4,379,278 were permitted to operate in the cycling mode, it would be subject to the same short circuiting problems as other prior art circuit breakers. To prevent this dangerous condition from occurring between the coacting contacts, this patent discloses an insulating and reset device which on opening movement of the contacts slides between the coacting contacts, and remains in this position until it is manually reset after the cause of the overload condition is corrected in the associated current carrying circuit being protected by the circuit breaker.
In this U.S. Pat. No. '278 a relatively small circuit breaker having high stability, smooth and accurate operation within the desired calibration for operation, and close tolerance during manufacture was achieved by having staggered terminals and by mounting the bimetallic actuator transversely therebetween so that the insulating and reset device and its actuating spring can be disposed coaxially to each other in the center line of the circuit breaker to insure the desired smooth operation both under adverse conditions in the circuit and on reset to place the circuit breaker back into operation in the associated current carrying circuit.
However, the circuit breaker disclosed does not provide sufficient room for the coacting elements to enable it to be miniaturized to the dimensions required for replacement or for retrofitting this device in place of a conventional blade or clip type fuses used to prevent overloads in an associated current, carrying circuit.
The present invention provides an improved circuit breaker utilizing a "Taylor Type" thermally operated snap acting bimetallic actuator which is standardized to operate in a cycling mode or may be converted very simply to a non-cycling mode by adding an insulating and reset slide or member disposed to move between the coacting contact elements of the bimetallic actuator when the contacts are moved from the normally closed position to the open position. In this improved circuit breaker the elements are so arranged that the size of the circuit breaker can be reduced and miniaturized to enable this circuit breaker to replace or to be retrofitted in place of the conventional blade or clip type fuses for limiting current overload in an associated current carrying circuit.
In the present invention in order to achieve this desirable end and to provide a circuit breaker capable of being manufactured and assembled for either the cycling mode or the non-cycling mode, the terminals and the bimetallic actuator are disposed in the limited space available in the housing for the circuit breaker in alignment with each other and parallel to the longitudinal line of the housing, the housing also having sufficient room to provide means, in the case of a non-cycling circuit breaker for adding or assembling an insulating and reset slide or member in a position offset from and overlapping at least one of the aligned terminals to permit movement parallel to the same longitudinal line of the housing for the circuit breaker so that the insulating and reset assembly can provide the same advantageous operation as is achieved in U.S. Pat. No. '278.